A Lathe Tool Bit Question

[Downwindtracker2]

Good Morning, I hope this finds you well after last night's victory.

A question at the pointy end for experts.. Yesterday I was looking for a grind that gave a good surface finish .(aren't we all) So I honed a bit carefully.I was happy enough with the sharp. It wasn't one I had ground, rather an estate auction pick up. Just for background I spun the 5/8" CRS for 80sfm with, .005" travel. I had weld at the tip, when I knocked it off I could see deposits on the face. It was a good Armstrong brand HSS bit. I used Gunk brand high sulfur cutting oil.

How do I avoid the welding, I'm set up coolant, but don't use it.

 

[thestelster]

Reduce speed, hone the tool bit, use coolant.

 

[Arbutus]

Without seeing the tool and the relief, your description implies that there is too much heat at the cutting tip, which is related to cutting speeds and the two top rake angles and the relief angle.

Top rake should be 3-5 degrees. For the side relief, I rely on the grinding wheel curvature with the top edge of the tool above the wheel centre. The relief angles are about 2 degrees. The top face is usually honed with a slip stone after grinding with a 320 grit diamond wheel.

Try regrinding with a larger relief and top rake.

 

[Susquatch]

I note you said hss, not carbide.

I assume turning, not facing.

Can you post a photo of your tool in position on the work?

 

[Downwindtracker2]

This was a very aggressive bit he made.It's certainly not one I made at college. I'm looking at 16* across the top and at least couple front to back. Hard to measure that one.The side relief was healthy 5*. A nose radius of 1/64". I set QCTP so the included angle was about 90*

Looking at closely , I was bit optimistic to use it on steel, even after all that honing. But it still brings it back to dealing with heat build up.

 

[Susquatch]

Looking at closely , I was bit optimistic to use it on steel, even after all that honing. But it still brings it back to dealing with heat build up.

I really need to see photos. If you can't do that for some reason, then at least try to make a hand drawing for us.

Regarding heat, plowing steel creates heat. There is no getting around that. But a proper cutting tool puts the heat into the chip so it can be carried away. I don't think you are creating too much heat. You just are not getting rid of it.

 

[Downwindtracker2]

I'm sorry, I don't know how to move photos from my phone, I barely know how to take photos in the first place, to the computer, then on to forum.

But what you said triggered the thought process. Thank You ! My Gawd that part is painfully rusty. The hot chips are piling up on the face and basically melting into the bit. The cutting edge geometry is at fault. As you say, it should be moving the chips away. I dug into my textbooks, they didn't have much in the way of background to give an understanding.

Now that I have a working lathe, it has to do some work. One of the early projects are rifle cartridge case brass expanders for a Stoney Point cartridge overall length gauge. Both size, in the 1/10s, and the finish are critical. I have some odd ball calibers.

 

[Arbutus]

This may help: https://littlemachineshop.com/reference/rakerelief.php

 

[Downwindtracker2]

I have number of 3/8' tool bit blanks. I'll try grinding one, instead of using someone else's attempt.

I'll use the coolant pump. Any recommendations on soluble oil brand ?